Waste heat boiler



' Sept. 8, 1931. A M. HARKNESS WASTE HEAT BOILER Filed Aug. 24

INVENTOR ATTORNEY Patented Sept. 8, 1931 UNITED. STATES PATENT" OFFICE ANDREW Iv'I. HARKNESS, OF NYACK, NEW YORK, ASSIGNOR TO GENERAL CHEMICAL COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK WASTE HEAT BOILER Application filed August 24, 1927.

This invention relates to heat-transfer systems, and more particularly to waste heat boilers.

In the manufacture of sulfuric acid by the contact process the primary gases (S0 0 etc.) from which the sulfuric acid is ultimately formed meet a high temperature when they leave the pyrites or brimstone burners. In order for the catalytic action which converts these gases to sulfur trioXide to take place eticiently the temperature of these primary gases should undergo a substantial reduction prior to their being admitted to the catalytic converters.

It has been suggested to utilize in this relation a heat transferrer of the waste heat boiler type by means of which the temperature of the gases could be effectively re duced, and the heat absorbed made use of for the generation of power or other purposes. The peculiarities of sulfuric acid manufacture, however, render the ordinary waste heat boilers but poorly suited for this pur pose.

The ordinary waste heat boilers are commonly characterized by the fact that the conduit pipes, which conduct the gases etc. through the cooling medium, are secured to the jacket of the cooling chamber at a plurality of points, usually at both ends, and these conduits are generally arranged'horizontally within the chamber. By reason of this customary rigid securement of the conduits at a plurality of points, the possibility is always present of the conduits becoming disrupted, or released from their fastenings because of uncompensated expansion or contraction due to temperature changes.

The leaks caused by such disruption or release would not be particularly detrimental in ordinary applications of the boiler, unless the leakage were of considerable magnitude, but in sulfuric acid systems, such for eX- ample as those based on the contact process, even a slight leakage within the boiler would present serious aspects. The water or steam thus admitted into the system in which sulfuric anhydride is produced would jeopardize the entire apparatus and process, the cor rosion factor presented thereby being alone Serial No. 215,027.

deposition on the walls of the conduit, pars ticularly at the bottom, with a resultant diminution in the heat transfer eiiiciency of the conduit. This dust layer, furthermore, promotes condensation of sulfuric acid from the gases, some slight amount of which is always present even prior to the catalytic conversion step, and the condensed acid at tacks the steel of which the conduit is constructed. By the formation of a dust layer a region insulated from the hot gases in the conduit is provided between such layer and the externally cooled, highly conductive wall of the conduit,and into this cooled region the sulfuric acid will penetrate and will condense when the temperature of the cooling medium in contact with the conduit wall too closely approaches that at which sulfuric acid will condense (approximately 400 F.).

The object of my invention is to provide an improved construction in a heat transfer system of the waste-heat boiler type which will include proper provision for expansion and contraction of the conduits which are in contact with the heat transfer medium within said boiler.

A further object of my invention is to provide a construction of the order noted in which the possibility of dust deposition within said conduits, and the formation and retention of condensation products therein will be reduced to a minimum.

With the above and other objects in View, the manner in which I accomplish the same will be apparent from the following specification taken in conjunction with the accompanying drawings in which Fig. 1 is a vertical sectional view of a waste heat boiler embodying my invention, with parts broken away, and

Fig. 2 is a horizontal section of the same, taken along the line 22, Fig. 1.

Referring to the drawings, and in particular to Figure 1, reference numeral 3 designates a steel outer shell or acket which defines the cooling chamber 4, of a waste heat boiler, the bottom of which jacket is flanged as at 5 to form openings 6, these flanges providing foundations for the securement of a pair of conduit pipes 7, 8 constituting the arms of an inverted U-shaped steel conduit 9. The upper ends of the pipes 7, 8 constituting the arms of the inverted U-shaped conduit are connected together by a coupling 10, riveted or otherwise secured thereto.

The mounting of the conduit 9 in the chamber 4c is characterized by the restriction of the securement of its arms to the flanges 5 to a substantially localized area or point in the length of each arm, by rivets 11 or other means, the portion of the conduit above the area of securement being left substantially unsecured. It will be seen that by this arrangement the arms of the inverted U-shaped conduit are secured to the jacket only over localized areas located respectively at the points of entry of the arms into the jacket; the portion of the conduit projecting into the chamber, and particularly the terminus of said projecting portion (in this instance the top of the inverted U) being left free of securement. This conduit is mounted within the chamber l for conducting therethrough the gases to be cooled (i. e. S0 O etc), the gases entering and passing upwardly through the passage in the arm 7, and downwardly through the passage in the arm 8, whence they are conducted to the converters to be converted into sulfur trioxide.

A feed pipe 12 is mounted in a bushing in the wall of jacket 3 and leads into the chamber 4 for introducing therein the water or other heat transfer medium, and in the top of the acket 3, a pair of steam nipples 13 and l t are provided, the nipple 13 serving as an outlet for the steam or vapor generated in the boiler and the nipple 14 being connected with a suitable safety valve (not shown). The usual manhole 15, handholes l6, and blow off opening 17 are provided for affording access to the interior of the jacket for cleaning and repairing the same. Reference numerals 18 and 18' designate respectively the usual pressure and water gauges which may be of any suitable and well-known type. I

In the boiler of the present application I use two conduits 9, as best shown in Figure 2, although any desired number may be provided. For maintaining these rather eloir gated conduits in proper vertical relation, I provide, supplementary to be localized securing means 11, a guiding brace 19. This brace 19 consists of an outer frame ork 20 riveted or otherwise attached to the jacket 3, to which frame work a series of suitable steel. straps 21 are secured, each strap confining}; one of the arms 7, 8 of the conduits 9 between itself and the adjoining sides of the frame work 20. This brace eliminates the possibility of the conduit pipes 9 working loose from or weakening their connection with the flanges 6 by leaning away from the original vertical position in which they were seem-ed. The straps 21 but lightly contact with the conduits 9 and oli'er no appreciable resistance to expansion or contraction of said conduits, their function being simply to maintain the couduits in position and not to secure them.

When the boiler is in operation the conduits are completely covered by the water or other heat transfer medium as indicated by the water level shown by the dotted line in Fig. 1.

The construction I have described provides a very efiicient wasteheat boiler and satisfactorily eliminates the dangers arising from er:- pansion or contraction, and corrosion of the conduits. By means of the localized securement of the conduit, leaving its major portion and the inner terminus of the portion pro jecting into the chamber with no impediment to expansion or contraction, there is no tendency toward disruption on the part of the conduit arising from external resistance to its longitudinal expansion or contraction. The free upper portion of the conduit will present an outlet or take-up for the longitudinal. expansion or contraction in the conduit produced by even considerable temperature changes with no deleterious effects upon the conduit or its securement to the acket.

In addition, such a construction permits the use of riveted, welded, or screwed joints in the securement of the conduit to the jacket, rather than the common rolled oints, which exhibit a tendency toward reac y leakage.

Further, the vertical arrangement of the passages in the conduit pipes affords but slight opportunity for a dust coating being formed, and such inclination as there might be toward a dust deposition in the limited horizontal area provided by the coupling section 10 is opposed by the strong eddy currents prevailing in the section 10 and by the rounded character of the lower part of the section. The continuous, vertical conduit passages in the cooling chamber reduce the horizontal travel of the gases while in the cooling chamber to a minimum. and thus avoid any ap preciable deposition of dust in the conduit within the cooling chamber.

The inverted U-shaped type of conduit which I employ presents a type of 0011991110 tion which affords a maximum of vertical structure with a minimum of horizontal structture, a relation extremely desirable in the present application, and such an arrange ment presents a very extensive exposed length of conduit to the cooling medium which entirely surrounds the same while occupying but a comparatively small. space. The inverted U-shapcd conduit construction is particularly well adapted, moreover, for the localized securement desired, the attachment of the conduit at the lower portion of the arms of the U presenting a very stable two point supporting arrangement.

It will be clear that while I have shown the U-shaped conduit as constructed of a plurality of elements, it may be formed as a single element.

In referring to the conduit as having the shape of an inverted U I mean simply a construction having the general conformation of a U, whether the arms be vertical or otherwise, so positioned in respect to the attaching medium, in this instance the boiler jacket 3, that the bend or curve of the U is spaced from said medium by the arms of said U.

W' hen I refer to the conduit pipes as unaligned I mean that the longitudinal axes of the pipes do not lie in a single straight line.

While I have stressed the applicability of my waste-heat boiler particularly in relation to sulfuric acid roduction, it is obvious that the troublesome factors indicated, which are over onie by my construction, are not neces sarily confined solely to the production of that material, and the solution which the construction offers to the basic elements of the problem is equally applicable, with reasonable modifications, to apparatus used in other and similar relations.

The foregoing discloses a preferred embodiment of my invention, but it is to be understood that. I do not limit myself to the specific form disclosed and consider my invention to contemplate all equivalent constructions and arrangements of parts such as may fall within the scope of the appended claim.

I claim:

A waste heat boiler for cooling hot dustladen gases in the contact process of making sulfuric anhydride comprising an enclosing shell adapted to contain water and steam 1111- der pressure, said shell having opposing end walls, a plurality of U-shaped gas conduits projecting into said shell through an end wall and attached thereto, and free from the end wall of the shell most remote from the point of attachment of the conduits, said conduits being entirely below the water level in said shell and having an inner contour such as to operate in conjunction with the gas currents passing therethrough against the deposition of substantial amounts of dust on the inner portions of said conduits within the shell, a steam outlet associated with the shell above the liquid level therein, and means including bracing elements loosely engaging the conduits and attached to the shell for maintaining said conduits in substantially the position in which they are secured to said shell.

In testimony whereof, I afiix my signature.

ANDREW M. HARKNESS. 

